America has stepped up its investigation into the market-rigging scandal engulfing the banking sector by sending a team to London to question bankers over the alleged manipulation of foreign exchange benchmarks.

Authorities from the US Federal Reserve and Office of the Comptroller of the Currency have been paying visits to the Canary Wharf offices of Citigroup to interview employees.

The bank has also been combing through e-mails and chat room correspondence between traders looking for evidence of market manipulation.

Citigroup declined to comment.

Meanwhile, Deutsche Bank has suspended a group of traders in New York after finding evidence of possible